Advani became a member of the Bharatiya Jana Sangh, also known simply as the Jana Sangh, which was founded in 1951 by Syama Prasad Mookerjee in collaboration with the RSS. He was appointed as the secretary to S. S. Bhandari, then General Secretary of the Jana Sangh in Rajasthan. In 1957, he was moved to Delhi to look after the Parliamentary affairs. He soon became the General Secretary and, later, President of the Delhi unit of the Jana Sangh. After the 1967 elections, he became the leader of the city's Metropolitan Council. He also assisted K. R. Malkani in editing the RSS weekly Organiser, and became a member of the national executive in 1966.[6]

He became member of the Rajya Sabha from Delhi for the six-year tenure from 1970.[7] After serving various positions in the Jana Sangh, he became its President in 1973 at the Kanpur session of the party working committee. His first act as president of the BJS was to expel founder member and veteran leader Balraj Madhok from primary membership of the party for supposedly violating the party directives and acting against the interests of the party. He was a Rajya Sabha member from Gujarat from 1976 to 1982.[7] After the Indira Gandhi's Emergency, the Jana Sangh and many other opposition parties merged into the Janata Party. Advani and colleague Atal Bihari Vajpayee fought the Lok Sabha Elections of 1977 as members of the Janata Party.

The Janata Party was formed by political leaders and activists of various political parties who had been united in opposing the state of Emergency imposed in 1975 by then-Prime Minister Indira Gandhi. After elections were called in 1977, the Janata Party was formed from the union of the Congress (O), the Swatantra Party, the Socialist Party of India, the Jana Sangh and the Lok Dal. Jagjivan Ram split from the Indian National Congress, bringing a small faction known as the Congress for Democracy with him, and joined the Janata alliance. The widespread unpopularity of Emergency rule gave the Janata Party and its allies a landslide victory in the election. Morarji Desai became the Prime Minister of India, Advani became the Minister of Information and Broadcasting and Vajpayee became the Foreign Minister.

The erstwhile members of the Jana Sangh, quit the Janata Party and they formed the new Bharatiya Janata Party. Advani became a prominent leader of the newly founded BJP and represented the party in the Rajya Sabha (upper house of the Indian Parliament) from Madhya Pradesh for two terms beginning in 1982.[4][7]

Atal Bihari Vajpayee was appointed the first president of the new party. Historian Ramachandra Guha writes that despite the factional wars within the Janata government, its period in power had seen a rise in support for the RSS, marked by a wave of communal violence in the early 1980s.[8] Despite this, the BJP under Vajpayee initially took a more moderate approach to Hindutva, to gain a wider appeal. This strategy was unsuccessful, as the BJP won only two Lok Sabha seats in the elections of 1984.[9] A few months prior to the election, Indira Gandhi was assassinated, creating a sympathy wave for the Congress that also contributed to the BJP's low tally, as the Congress won a record number of seats. This failure led to a shift in the party's stance; Advani was appointed party president, and the BJP returned to the hardline Hindutva of its predecessor.[10]

Under Advani, the BJP became the political face of the Ram Janmabhoomi campaign. In the early 1980s, the Vishwa Hindu Parishad (VHP) had begun a movement for the construction of a temple dedicated to the Hindu deity Rama at the site of the Babri Masjid in Ayodhya.[11] The agitation was on the basis of the belief that the site was the birthplace of Rama, and that a temple once stood there that had been demolished by the Mughal emperor Babur when he constructed the Babri mosque. The Archaeological Survey of India (ASI) has supported the claim that a Hindu structure once stood at the site, without commenting on a possible demolition.[12][13] The BJP threw its support behind this campaign, and made it a part of their election manifesto, which provided rich dividends in the general elections of 1989. Despite the Congress winning a plurality in the election, it declined to form a government, and so the National Front government of VP Singh was sworn in. The support of the BJP, with its tally of 86 seats, was crucial to the new government.[14]

Advani embarked on a "Rath Yatra," or chariot journey, to mobilise karsevaks, or volunteers, to converge upon the Babri Masjid to offer prayers. This Rath Yatra, undertaken in an air-conditioned van decorated to look like a chariot, began from Somnath in Gujarat and covered a large portion of Northern India until it was stopped by the Chief Minister of Bihar, Laloo Prasad Yadav, on the grounds that it was leading to communal violence. In the 1991 general elections, the BJP won the second largest number of seats, after the Congress.

In 1992, two years after Advani ended his yatra, despite assurances given by the Kalyan Singh led BJP Government to the Supreme Court, the Babri Masjid was demolished by the nationalists with alleged complicity of the Kalyan Singh government.[15][16] Advani is one of the main accused in the Babri Masjid case.[17]

BJP, under Advani, sat in the opposition from 1991–1996 during the reign of P V Narasimha Rao. The Rao regime was repeatedly accused by the BJP of corruption and various scandals.

After the 1996 general elections, the BJP became the single largest party and was consequently invited by the President to form the Government. Atal Bihari Vajpayee was sworn in as Prime Minister in May 1996. However, the Government did not last long and Vajpayee resigned after thirteen days.

After two years in the political wilderness, the BJP-led National Democratic Alliance (NDA), came to power with Vajpayee returning as Prime Minister in March 1998, when elections were called after India saw two unstable Governments headed by H. D. Deve Gowda and I. K. Gujral respectively.

After the fall of two United Front government between 1996 and 1998 (H. D. Deve Gowda and I. K. Gujral), the Lok Sabha, (lower house) of India's Parliament was dissolved and new elections were held. Now, a coalition of political parties signed up with BJP to form the Nationwide Democratic Alliance (NDA), headed by A.B. Vajpayee. The NDA won a majority of seats in parliament. However, the govt survived only 13 several months until mid-1999 when All Indian Anna Dravida Munnetra Kazhagam (AIADMK) under J. Jayalalitha withdrew its assistance to govt. With the NDA no longer having a majority, India's Parliament was again dissolved and new elections were organised. Vajpayee remained the Prime Minister until elections were organised.

Advani assumed the office of Home Minister and was later elevated to the position of Deputy Prime Minister. As Union Minister, Advani had a tough time with India facing a string of internal disturbances in the form of rebel attacks allegedly supported by Pakistan. The NDA government lasted for its full term of five years till 2004, the only non-Congress government to do so.

Advani was charged in a scandal where he allegedly received payments through hawala brokers. He and others were later discharged by the Supreme Court of India, because there was no additional evidence which could be used to charge them.[18] According to the judicial inquiry by Central Bureau of Investigation (CBI) they could not find any substantive evidence; the Supreme Court ruling stated that no statement even mentioned Advani's name and that evidence against him was limited to the mention of his name on a few loose sheets of paper.[18]

However, the failure of this prosecution by the CBI was widely criticised.[19] While some believe the CBI probe catapulted his rise through the BJP on his newfound "moral authority",[20] others have claimed the inquiry was a political stunt.[21][22]

As elections approached in 2004, Advani was supremely confident and conducted an aggressive campaign where he claimed the Congress Party would not get even 100 seats. The BJP suffered a defeat in the general elections held in 2004, and was forced to sit in the opposition. Another coalition, the United Progressive Alliance led by the resurgent Congress came to power, with Manmohan Singh as Prime Minister. The NDA disintegrated with the Telugu Desam Party, which had supported the NDA government from the outside, deserting the alliance.

Vajpayee retired from active politics after the 2004 defeat, putting Advani to the forefront of the BJP. Advani became Leader of Opposition in the Lok Sabha from 2004 to 2009. During this period, Advani had to deal with rebellion from within the party. His two close associates, Uma Bharati, and Madan Lal Khurana, and longtime rival Murali Manohar Joshi publicly spoke out against him. In June 2005, he drew much criticism when he, while on a visit to the Jinnah Mausoleum at Karachi – his town of birth, endorsed Mohammad Ali Jinnah and described him a "secular" leader. This did not sit well with the RSS either and Advani was forced to relinquish his post as BJP president. However, he withdrew the resignation a few days later.

The relationship between Advani and the RSS reached a low point when the latter's chief K. S. Sudarshan opined that both Advani and Vajpayee give way to new leaders.[23] At the Silver Jubilee celebrations of the BJP in Mumbai in December 2005, Advani stepped down as party president and Rajnath Singh, a relatively junior politician from the state of Uttar Pradesh was elected in his place. In March 2006, following a bomb blast at one of the holiest Hindu shrines at Varanasi, Advani undertook a "Bharat Suraksha Yatra" (Sojourn for National Security), to highlight the alleged failure of the ruling United Progressive Alliance in combating terrorism.

Advani discussing black money in a rally during the election campaign of 2009.

In an interview with a news channel in December 2006, Advani stated that as the Leader of the Opposition in a parliamentary democracy, he considered himself the Prime Ministerial candidate for the general elections, ending on 16 May 2009.[24] Some of his colleagues were not supportive of his candidacy.[25]

A major factor in favour of Advani was that he had always been the most powerful leader in the BJP with the exception of Vajpayee, who endorsed Advani's candidacy. On 2 May 2007, BJP President Rajnath Singh stated that: "After Atal there is only Advani. Advani is the natural choice. It is he who should be PM".[26] On 10 December 2007, the Parliamentary Board of BJP formally announced that L. K. Advani would be its prime ministerial candidate for the general elections due in 2009.

Advani unexpectedly resigned from all his posts in the BJP on 10 June 2013 following the appointment of Narendra Modi as the head of the electoral campaign of BJP for the 2014 elections on 9 June 2013. He rued that the BJP was no longer the "same idealistic party" created by Shyama Prasad Mookerjee, Deendayal Upadhyaya, Nanaji Deshmukh and Atal Bihari Vajpayee. The BJP senior committee rejected his resignation on 10 June 2013. Ultimately, Advani withdrew his resignation on 11 June 2013 after Rajnath Singh (BJP President) assured Advani that his concerns about the functioning of the Party would be properly addressed.

Popularly known in India as the Eternal yatri or Eternal Charioteer,[30] L. K. Advani has so far, undertaken 6 yatras throughout India.

Ram Rath Yatra: Advani started his first Rath Yatra from Somnath, Gujarat[31] on 25 September 1990 to finally reach Ayodhya on 30 October 1990. The yatra has been linked to the Mandir-Masjid dispute centred around Ram Janmabhoomi-Babri Masjid site at Ayodhya. The BJP and Advani, however, focused the yatra on the secularism–communalism debate.The yatra was stopped in Bihar by Lalu Prasad Yadav.

Janadesh Yatra: Four Yatras named Janadesh Yatra[32] started on 11 September 1993 from four corners of country. Advani led this yatra from Mysore. Travelling through 14 States and two Union Territories, the yatris congregated at Bhopal on 25 September in a massive rally. The purpose of Janadesh Yatrawas to seek the people's mandate against the two Bills, the Constitution 80th Amendment Bill and the Representation of People (Amendment) Bill.[33]

Swarna Jayanti Rath Yatra: The Swarna Jayanti Rath Yatra by Mr. Advani travelled across India between May and July 1997. According to Mr.Advani, the yatra was conducted in celebration of 50 years of Indian Independence and also to project the BJP as a party committed to good governance.[34]

Bharat Uday Yatra: The Bharat Uday Yatra took place in the run-up to the 2004 Lok Sabha Elections.[35]

Bharat Suraksha Yatra: The BJP launched a nationwide mass political campaign in the form of the Bharat Suraksha Yatra from 6 April to 10 May 2006. It consisted of two yatras – one led by Advani, Leader of the Opposition (Lok Sabha), from Dwaraka in Gujarat to Delhi; and the other led by Rajnath Singh, then the President of the BJP, from Jagannath Puri in Orissa to Delhi.[36] The yatra was focused on left wing terrorism, minority politics, corruption, protection of democracy and price rise.[37]

Jan Chetna Yatra: The Jan Chetna Yatra was launched on 11 October 2011 from Sitab Diara, Bihar. The BJP states the purpose of Jan Chetna Yatra is to mobilise public opinion against corruption of the UPA government and put BJP agenda of good governance and clean politics before the people of India.[38]

Khuswant Singh described Advani as "really one of the most able, cool-headed, courteous and clean politicians left today", and added that he is "pretty certain that he will never be unfair to Muslims if he becomes minister". [39]

"My Country My Life" is an autobiographical book by L. K. Advani. The book was released on 19 March 2008 by Abdul Kalam, the eleventh President of India. The book has 1,040 pages and narrates autobiographical accounts and events in the life of Advani. The book became a best seller in the non-fiction category. The book website claims that more than 1,000,000 copies have been sold. The book includes mentions of events in Indian politics and India's history from 1900 till 2007.